The steadfast Hubble Telescope takes the long view of space and time as it orbits the Earth, transmitting images of astronomical beauty and import.

Get a taste of what awaits you in print from this compelling excerpt.

It just keeps getting better. NASA's Hubble space telescope, with a new camera installed in March 2002, reveals the cosmos more clearly than ever before. The satellite orbits Earth every 97 minutes and sends back exquisite views of a complex universe.

Hubble was built to be tuned up in orbit. But it wasn't designed for the major overhaul NASA astronauts undertook during its fourth servicing mission, 3B, in March 2002. They delved into the telescope's guts during long space walks and replaced parts that the original designers never thought they'd need to. Installation of a new power-control unit forced an unprecedented and nerve-racking shutdown of the entire satellitea move comparable to a surgeon stopping a patient's heart during surgery, says Anne Kinney, NASA's director of astronomy and physics. Astronaut John Grunsfeld raced to finish the task before the temperature of the switched-off telescope dropped far enough to damage it. Would it power back up? "When you run a computer for 12 years, you don't know what kind of ghosts you have in the system," Kinney says. When all systems reactivated as planned, the astronauts, as well as astronomers and mission controllers on the ground, breathed a collective sigh of relief.

The rest of the mission went like clockwork, including installation of a new cooling system for Hubble's near-infrared cameraNICMOSuseful for surveying dusty and cold areas of space, and installation of new solar panels and other science equipment.

It was the most challenging service mission ever attempted in space, and its success elated astronomers. Chief among the wonders was the long-awaited ACS, or Advanced Camera for Surveys. It essentially made Hubble into a new telescope. "ACS has roughly ten times the discovery power of the previous camera," says Mario Livio, astronomer at the Space Telescope Science Institute in Baltimore. Translation: Hubble can now see twice as much area with five times more light sensitivity.

Tragically, this mission would be the last successful voyage for space shuttle Columbia. The disaster in February 2003 grounded Discovery, Atlantis, and Endeavour, the three remaining shuttles, and will delay plans to bring Hubble a spectrograph and a new wide-field camera with ultraviolet and infrared capability.

With the human cost of sending people into space, should NASA rely more heavily on unmanned alternatives for exploration?

In More to Explore the National Geographic magazine team shares some of its best sources and other information. Special thanks to the Research Division.

The Hubble Space Telescope was the first of the telescopes launched in NASA's Great Observatories program. Operational since 1990, it has been extraordinarily successful, making clear visible images of objects as near as Mars and as far as the edge of the known universe. The Compton Gamma Ray Observatory operated from 1991 until June 2000 when it was deorbited after the failure of a critical gyroscope. During its lifetime the observatory detected some of the most energetic objects in the universe, notably elusive gamma ray bursts. In 1999 the long-awaited Chandra X-Ray Observatory [See "Super X-Ray Vision."] was launched and has earned its keep with remarkable discoveries ever since. From its very high elliptical orbit, it sees wavelengths undetectable from Earth. Notably, Chandra provided sound evidence of the massive black hole at the center of our Milky Way galaxy. The fourth and final telescope of the program, SIRTF, designed to observe in infrared wavelengths that allow views through the dusty, cold reaches of the universe, was launched in August 2003.

You can read about the remarkable discoveries made by the Great Observatories in many popular publications or at the websites noted below. But perhaps you'd like to be more hands-on than that. With cold winter days ahead, how about making models of the observatories just for fun? You can find a kit provided by NASA Spacelink, an educational resource, at xsl.msfc.nasa.gov/products/NASA's.Great.Observatories.KitThe kits are tailored for grades 5 through 12, but I'm guessing there are a lot of would-be engineers who would get a kick out of assembling an accurate model of a space-borne telescope. Be sure to get the propellant tanks, instrument assemblies, and antennas in the right place!

Compton Gamma Ray Observatorycossc.gsfc.nasa.gov/index.htmlThis is the home page for the second of the Great Observatories. CGRO operated from 1991to 2000, imaging the universe's most energetic phenomena.

Chandra X-ray Observatorychandra.harvard.edu/index.htmlThis is the home page for the Great Observatory that images in x-ray wavelength. It includes links to images, history, and the latest information about the telescope.

SIRTF Science Centersirtf.caltech.edu/SSC/This site contains all information on the last of the Great Observatories, the Space Infrared Telescope Facility, which observes astronomical objects in the infrared.

NASA Space Sciencespacescience.nasa.gov/index.htmHere you will find a gateway to information and images on the solar system, astronomy, cosmology, and space science missions.